Hitler lost the 1932 presidential election to Paul von Hindenburg, but the Nazi Party became the largest party in the Reichstag after the 1932 elections. Hitler was later appointed Chancellor, and then after the Reichstag Fire, a law was enacted that gave the Nazis considerable power to force their political opposition to shut down. The Enabling Act was passed in March 1933, giving the Chancellor (Hitler) the powers of the Reichstag...pretty much giving him the dictatorial rights that he is known for. By the middle of 1933, all political parties except for the Nazi Party were banned. After von Hindenburg died in 1934, Hitler merged the offices of the Chancellor and the President, creating a new office: the Führer. He was still referred to as the "Führer und Reichskanzler", though.
It's a dark chapter in human history, and we've got to make sure that we don't let anything like it happen again.
So: Hitler came to power in 1933 and ruled as Führer from 1934 to his death in April 1945.